Friction (CH 12) and Sound (CH 13), CLASS 8

 1. A list of mediums is given below.

(i) wood

(ii) water

(iii) air

(iv) vacuum

In which of these mediums can sound travel?

(a) i & ii only

(b) i, ii & iii only

(c) iii & iv only

(d) ii, iii & iv only

2. The loudness of a sound depends on:

(a) its amplitude.

(b) its frequency.

(c) its time period.

(d) its speed.

3. Which of the following statements are correct?

(i) Sound is produced by vibrations.

(ii) Sound requires a medium for propagation.

(iii) Light and sound both require a medium for propagation.

(iv) Sound travels slower than light.

(a) i & ii only

(b) i, ii & iii only

(c) ii, iii & iv only

(d) i, ii & iv only

4. An object is vibrating at 50 hertz. What is its time period?

(a) 0.02 s

(b) 2 s

(c) 0.2 s

(d) 20.0 s

5. In order to reduce the loudness of a sound, we have to

(a) decrease its frequency of vibration of the sound.

(b) increase its frequency of vibration of the sound.

(c) decrease its amplitude of vibration of the sound.

(d) increase its amplitude of vibration of the sound.

6. The loudness of sound is determined by the

(a) amplitude of vibration

(b) the ratio of amplitude and frequency of vibration

(c) frequency of vibration

(d) product of amplitude and frequency of vibration

7. 1 hertz is equal to

(a) 1 vibration per minute

(b) 10 vibrations per minute

(c) 60 vibrations per minute

(d) 600 vibrations per minute

8. Pitch of sound is determined by its

(a) frequency

(b) amplitude

(c) speed

(d) loudness

9. Ultrasound has a frequency of vibration

(a) between 20 and 20,000 Hz

(b) below 20 Hz

(c) above 20,000 Hz

(d) between 500 and 10,000 Hz

10. Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play

(a) only if the objects are solid.

(b) only if one of the two objects is liquid.

(c) only if one of the two objects is gaseous.

(d) irrespective of whether the objects are solid, liquid or gaseous.

11.  To sharpen the blade of a knife by rubbing it against a surface, which of the following will be most suitable?

(a) stone

(b) plastic block

(c) wooden block

(d) glass block

12. If we apply oil on door hinges, the friction will

(a) increases

(b) decreases

(c) disappear altogether

(d) will remain unchanged

13. Which of the following statements is incorrect?

(a) Friction acts on a ball rolling along the ground.

(b) Friction acts on a boat moving on water.

(c) Friction acts on a bicycle moving on a smooth road.

(d) Friction does not act on a ball moving through air.

14. A boy rolls a rubber ball on a wooden surface. The ball travels a short distance before coming to rest. To make the same ball travel longer distance before coming to rest, he may

(a) spread a carpet on the wooden surface.

(b) cover the ball with a piece of cloth.

(c) sprinkle talcum powder on the wooden surface.

(d) sprinkle sand on the wooden surface

15. In a large commercial complex, there are four ways to reach the main road. One of the paths has loose soil, the second is laid with polished marble, the third is laid with bricks and the fourth has a gravel surface. It is raining heavily and Paheli wishes to reach the main road. The path on which she is least likely to slip is

(a) loose soil.

(b) polished marble.

(c) bricks.

(d) gravel.

16. Two boys are riding their bicycles on the same concrete road. One has new tyres on his bicycle while the other has tyres that are old and used. Which of them is more likely to skid while moving through a patch of the road which has lubricating oil spilt over it?

17.  Imagine that an object is falling through a long straight glass tube held vertical; the air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?

18. Lightning can be seen as the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s).

19. Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give the reason for the delay in hearing the sound.

20. A simple pendulum makes 10 oscillations in 20 seconds. What is the time period and frequency of its oscillation?

CLASS TEST CH - 11,12 (CLASS 6)

1 . Observe the picture given in fig 11.1 carefully.

A patch of light is obtained at B, when the torch is lighted as shown. Which of the following is kept at position A to get this patch of light?
(b) A glass sheet
(c) A mirror
(d) A sheet of white paper,

2. A student observes a tree given in figure through a pinhole camera. Which of the diagrams given in figures (a) to (d) depicts the image seen by her correctly?

3. Four students A, B, C and D looked through pipes of different shapes to see a candle flame as shown in fig 11.4.

Who will be able to see the candle flame clearly?
(a) A
(b) B
(c) C
(d) D

4 Which of the following is/are not always necessary to observe a shadow?
(a) Sun
(b) Screen
(c) Source of light
(d) Opaque object

5. Paheli observed the shadow of a tree at 8:00 a.m., 12:00 noon and 3:00 p.m. Which of the following statements is closest to her observation about the shape and size of the shadow?
(a) The shape of the shadow of the tree changes but the size remains the same.
(b) The size of the shadow of the tree changes but the shape remains the same.
(c) Both the size and shape of the shadow of the tree change.
(d) Neither the shape nor the size of the shadow changes.

6. Which of the following can never form a circular shadow?
(a) A ball
(b) A flat disc
(c) A shoe box
(d) An ice cream cone

7. Two students while sitting across a table looked down on to its top surface. They noticed that they could see their own and each other’s image. The table top is likely to be made of
(a) Unpolished wood
(b) Red stone
(c) Glass sheet
(d) Wood top covered with cloth

8. Choose from the options a, b, c and d given in the fig 12.1 which shows the correct direction of current.

9. Choose the incorrect statement.
(a) A switch is the source of electric current in a circuit.
(b) A switch helps to complete or break the circuit.
(c) A switch helps us to use electricity as per our requirement.
(d) When the switch is open there is an air gap between its terminals.

10. In an electric bulb, light is produced due to the glowing of
(a) the glass case of the bulb
(b) the thin filament
(c) the thick wires supporting the filament
(d) gases inside glass case of the bulb.

11. In the following arrangement shown in fig 12.2, the bulb will not glow if the ends A and B are connected with

(a) A steel spoon
(b) A metal clip
(c) A plastic clip
(d) A copper wire

12. In the circuit shown in fig 12.3, when the switch is moved to ‘ON’ position,

(a) the bulb A will glow first
(b) the bulb B will glow first
(c) the bulb C will glow first
(d) all bulbs will glow together

13. Filament of a torch bulb is
(a) a metal case
(b) metal tip at the centre of the base
(c) two thick wires
(d) a thin wire

14. Paheli is running short of connecting wires. To complete an electric circuit, she may use a
(a) glass bangle
(b) thick thread
(c) rubber pipe
(d) steel spoon

15. In which of the following circuits A, B and C given in fig 12.4, the cell will be used up very rapidly?

16. Correct the following statements.                                  (2)

(i) The colour of the shadow of an object depends on its colour of the object.
(ii) Transparent objects allow light to pass through them partially.

17. An electric bulb is connected to a cell through a switch as shown in fig 12.7. When the switch is brought in ‘ON’ position, the bulb does not glow. What could be the possible reason/s for it? Mention any two of them.                                                     (3)